$-\dfrac{2}{10} + \dfrac{1}{4} = {?}$
Solution: $ = - {\dfrac{2 \times 2}{10 \times 2}} + {\dfrac{1 \times 5}{4 \times 5}} $ $ = - {\dfrac{4}{20}} + {\dfrac{5}{20}} $ $ = - \dfrac{{4} + {5}}{20} $ $ = \dfrac{1}{20}$